The present invention relates to a modulating air flow controller and, more particularly, to a controller which yields the advantages of a proportional control system even though the input sensor is an on-off thermostat.
Traditionally, on-off control systems have had the advantage of fast response times and inexpensive construction. However, such control systems because of their fast response times tend to overshoot the control point which causes unstable control action. Proportional control systems were developed to provide stable control but are relatively more expensive to construct and result in slower response times in order to increase stability.
The present invention incorporates many of the advantages of both types of systems in a variable air volume setting in which proportional control is simulated in order to modulate the flow of air moving through an air supply duct in response to a simple on-off thermostat. Such a system does not require more complex proportional thermostats (i.e. thermostats having an output which is proportional to temperature deviation from a setpoint) and associated control circuitry and does not have the instability problems of on-off control systems.